Regenerative processes in the skin require cross-talk of multiple cell signaling and epigenetic mechanisms; failure of this communication leads to a range of diseases from skin cancers to hair loss conditions. Delineating how these inputs are coordinated to impact gene expression at the level of chromatin has potential to identify novel therapies for skin dysfunction. Pioneer transcription factors initiate gene expression by binding nucleosome-enriched silent chromatin and recruiting chromatin modifiers to provide access for transcription machinery. Key regulatory genes in hair follicle stem cells are associated with ?super enhancers? containing binding sites for multiple transcription factors, suggesting that transcription factors activated in response to diverse signals collaborate with each other and with chromatin modifiers to coordinate cell-type specific transcriptional output. KLF4, a Krppel-like family member, has well-established functions as a pioneer transcription factor in iPS reprogramming, blocks Wnt/?-catenin signaling in intestinal epithelial cells, is required for normal differentiation of interfollicular epidermis, and is highly expressed in hair follicle stem cells. Opposite to KLF4, KLF5 promotes basal epidermal proliferation, and is required for Wnt/?-catenin signaling in intestine. KLF4 and KLF5 can directly repress each other's expression and KLF5 is absent from quiescent hair follicle stem cells, but is expressed in hair follicle matrix cells and in differentiating hair shaft cortex precursors that are highly Wnt-active.
The Aims of this proposal are: (1) to test the hypothesis that KLF4 integrates multiple signals to maintain hair follicle stem cell quiescence by (i) directly activating hair follicle stem cell quiescence genes, and (ii) complexing with TCF3/TCF4/HDAC to suppress Wnt targets; (2) to test the hypothesis that mutually antagonistic KLF4 and KLF5 functions control key transitions of hair follicle stem cells and their progeny. Genetic mouse models, and biochemical and genomics approaches will be used to address these questions.
Highly prevalent skin cancers such as squamous and basal cell carcinomas arise from hair follicles as well as from epidermal stem cells; therefore, delineating the controls of hair follicle stem cell function has relevance for understanding skin carcinogenesis as well as hair loss diseases. This project aims to determine how diverse signaling inputs are coordinated to impact transcription factor activity at the level of hair follicle stem cell chromatin, and has potential to identify novel therapeutic intervention points and targets.